The present invention pertains to a means of synchronizing the rotary shear and cutoff at order change in the dry end conversion of a corrugated web. In particular, the invention relates to a method for achieving a continuous web order change with the associated order change waste minimized and cut and slit so as to reduce potential for jam-up as it exits the cutoff knife into a stacking system.
In a corrugator dry end, where a corrugated paperboard web is longitudinally scored and slit into multiple parallel output webs (or “outs”), the outs are directed through one or more downstream cutoff knives which cut the output webs into selected sheet lengths. When two cutoff knives are used, they are vertically separated and each is capable of cutting the full corrugator width web. A web selector positioned downstream of the slitter/scorer divides the outs into two groups, one of which is directed to the upper cutoff knife and the other to the lower cutoff knife. Order changes must be effected while the upstream corrugator wet end continues to produce and deliver the continuous web to the slitter/scorer. An order change will typically result in a change in widths of the output webs, requiring redirection of at least a central portion of the web from one knife level to the other and possibly changes in edge trim widths as well.
The prior art has developed a gapless or plunge-style order change for corrugated dry ends utilizing double level cutoff knives. In this system, there are two slitter/scorer stations immediately adjacent to one another in the direction of web movement and through both of which the web travels. At order change, one slitter/scorer, operating on the currently running order, will lift out of operative engagement with the web, and the other slitter/scorer, which is set to the new order alignment, plunges down into operative engagement with the web. The result is a small order change region of corrugated web with overlapping slits and scores.
To effectuate such a gapless order change, a means must be provided to accommodate redirection of the central portion of the web in the web selector device from one knife level to the other. In U.S. Pat. No. 5,496,431, a laterally adjustable cutting tool, positioned over the center of the web, makes a cut in the order change region connecting the inner-most slit in the currently running order to the inner-most slit in the new order to allow a repositioning of the web directing forks in the web selector device.
In one embodiment of the above identified patent, the inner-most slits on the old and new orders are connected by a running diagonal cut to provide smooth transition in the output webs directed to the upper and lower cutoff knives. With this concept, there is a requirement to have overlapping slits on the outer edges of the web to allow straight lateral cut across the slits for a trim width change. Internal slits can be offset in the order change region in the running web direction, or overlapped. If the slits are offset, then the width of the scrap piece emerging from the cutoff knife may be wider than the individual outs on one level of the knife, creating a problematic situation upon discharge of the stack form that level. If the slits are overlapped, then there is potential for creation of small pieces, some of which have diagonal cuts that may not fit nicely on top of the stack onto which the cut sheets are directed.
In another embodiment of the above identified patent, the innermost slits of the old and new orders are connected by a lateral cut that requires the overlap of the innermost slits. By overlapping all slits, it is possible that the scrap associated with the order change region will emerge from the cutoff knife slit to the width of the old order sheets and a length shorter than the old order sheets so that these sheets are simply discharged into the top of the last stack in the old order, where they can be removed by the operator. Unfortunately, it is equally likely that several small odd-sized pieces may be created that will not have a stack to land on and that create high probability of a stacker jam-up. By only overlapping the innermost slits to create an opportunity for redirection of the webs at the web selector table and by controlling the cutoff knife to stop cutting prior to the order change region in the old order and after the order change region has passed on the new order it is possible to avoid the creation of small odd-sized pieces. The scrap piece created with this technique is typically larger than the sheets cut on the expiring order. In this case, the order change region scrap will not fit onto the top of the stack unless the stacker backstop is backed away when the scrap piece enters the stacker. This is problematic in that moving the backstop away to accommodate the long scrap sheet can allow sheets to cascade off the top of the stack onto the stacker lift.
To solve problems associated with order change region scrap removal, diverter systems have been installed after the cutoff knife. These knife diverters have been problematic because the space between cutoff knife levels constrains the distance between top and bottom knife diverters, making jam clearing very difficult. Diverting small pieces, some of which may have diagonal cuts, is also very challenging.
Another means of achieving a gapless order change while accommodating redirection of the central portion of the web in the web slitter device from one level to the other using a plunge slitter/scorer with two slitter/score stations is taught in U.S. Pat. No. 6,137,381. In this patent, a means of partially severing transversely across the web at a position prior to the slitter/scorer is utilized. The partial web sever is comprised of a transverse slit extending inwardly from one lateral edge that severs at least a portion of the web representative of the larger of the total width of the running and new order widths of one of the upper or lower output web portions. The innermost running order and new order output webs of the other of said upper and lower output web portions remain at least partially uncut by said transverse slit.
The partial web sever order change will result in that portion of the old order web that is cut by the transverse slit to accelerate away from the new order due to cutoff knife overspeed as soon as the transverse slit exits the slitter/scorer. This old order output web will be of the exact width of the expiring order and will be cut to length with the exception of a short tail scrap piece that will fit onto the top of the stack. The output web that has not been severed may have a change in the number and width of the outs from the old order to the new order. To prevent a small piece of scrap from being created at the end of the last cuts in the old order on this web, the cutoff knife must be biased to cut upstream of the transverse cut on this last cut of the old order. This approach prevents a short scrap piece from being created that may jam up. When doing this, a sheet is created with a leading edge that is not square under certain circumstances. This can also cause a jam-up at the stacker.